JPH0319471B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for liquefying hydrogen. [Prior art and its problems] Several methods have been proposed for industrially liquefying low molecular weight gases. Zeitschrift fiir Die Gesamte−Industrie39,
No. 6, 14-7 (1933), K.Clusius, “Plant for the production of liquid hydrogen with neon as an intermediate acting substance” describes the use of liquid air or liquid nitrogen as a precoolant and as an intermediate acting liquid. A method of liquefying nitrogen using high pressure neon and utilizing a high pressure Linde cycle is described. The article does not teach the use of expansion engine cycles such as those used in the Claude or Brayton cycles. U.S. Pat. No. 3,180,709 discloses a method for performing complex isenthalpic expansion (J-T valve) in combination with an expander in parallel,
A method of liquefying gases such as hydrogen, helium and neon is disclosed. US Pat. No. 3,473,342 describes, among other things, a method for liquefying large quantities of neon by cooling the compressed gaseous neon with liquid nitrogen. In that method, a portion of the cooled compressed neon is expanded in a turbo-expander to provide intercooling, and the remaining neon is expanded in a Juul-Thomson (J-T) expansion to produce liquefied neon. ing. Essentially, the cycle is a simple engine cloud cooler. US Pat. No. 3,609,984 describes a method for liquefying gases such as hydrogen, helium and neon.
Fundamentally, the method achieves liquefaction by compression of the gas, but the pressure is such that the compressed gas is expanded isentropically to form essentially a single liquid phase at atmospheric pressure. isobarically cooled to a temperature above the critical temperature of the gas that can be It creates a liquid phase. U.S. Patent No. 3992167 and Hydrogen Energy
Progress IV, Vol3, Pargamon Press (1982)
The section "Hydrogen Liquefaction Using Centrifugal Compression" by C.F. Baker discloses a method for liquefying hydrogen using a second component mixed with the hydrogen to utilize centrifugal compression. Both documents teach that high molecular weight gases are required to utilize centrifugal compression. U.S. Pat. No. 4,498,313 describes a helium cooling method and apparatus that precools helium gas and includes a neon gas cooling and liquefaction circuit using a turbine type compressor. The method is also
Utilizes liquid nitrogen for additional cooling overall efficiency. SUMMARY OF THE INVENTION The present invention provides an improved hydrogen liquefaction process that compresses and cools a hydrogen stream and catalytically converts predominantly ortho hydrogen to predominantly para hydrogen. provide law. This compressed, cooled, converted hydrogen stream is then expanded into an expander, thereby partially condensing the converted hydrogen stream. The partially condensed hydrogen stream is then separated into liquid and gas phases; the gas phase is warmed to restore cooling;
It is compressed and combined with the compressed hydrogen stream prior to conversion; the liquid phase is removed as a liquid hydrogen product. Improvements in the hydrogen liquefaction process include the use of dense fluid expanders to expand the converted hydrogen stream and the use of closed loop neon refrigeration cycles to provide intercooling for the liquefaction process. It's summery. Optionally, additional cooling is provided with liquid nitrogen to cool the compressed hydrogen stream or to pre-cool the neon in a closed circuit cooling cycle. Large scale liquefaction and refrigeration plants for the two cryogens, hydrogen and helium, require large compression systems. These systems must use positive displacement type compressors and expanders, respectively, due to the low molecular weight of both cryogens, ie 2 and 4. With the increasing demand for liquid hydrogen, especially for propellant fuels, the need for large scale production of hydrogen has become necessary. Units that achieve this large scale hydrogen production may be two to three times larger than existing implementation types. In order to effectively increase these growing demands, it is desirable to have a system that can be easily moved from one location to another with minimal modification. Their desirable characteristics of scale and ease of transfer have led to the development of hydrogen liquefaction systems using centrifugal compressors and expanders. Existing hydrogen liquefiers use volumetric displacement compressors. There are three main types of compressors that have been proposed for use in large scale hydrogen and helium systems. These are (a) Roots-type lobe blowers, (b) Lysholm-type axial screw compressors, and (c) reciprocating piston compressors. Primarily, the gas being compressed is a liquid, usually
There are several types, either with or without direct contact with oil, which functions as a lubricant or a combination of lubricant and coolant. Roots-type compressors are primarily used for subatmospheric suction applications of helium. These types of compressors provide modest compression rates per stage.
1.4-2.0 and limited to about 200 psig at relatively low maximum casting pressures. Lysholm oil-filled screw compressors, commonly used in helium systems, are inherently limited to pressures in the 300 psig range. These compressors have the advantage of having a high compression ratio per stage, ie up to 6, due to the effective cooling of the large amount of oil that circulates through the machine and is exchanged for water cooling. Its compressor is less energy efficient but less prone to gas leaks. Reciprocating compressors are used primarily for many helium systems, and especially for many hydrogen systems, because the high operating pressures for hydrogen liquefaction are, for example, 1200 psig. With recent advances, the energy efficiency of reciprocating compressors has improved. Unfortunately, because the reciprocating forces are not equal, these compressors must be mounted on a large foundation. Neither large screw type nor reciprocating compressors are compact. Screw compressors are usually skid mounted.
mounted), but on the other hand, they are limited to approximately 2250hp per aircraft. Large equipment may require a complex multi-parallel machine for each stage. A solution to the above problem of size lies in the use of centrifugal compressors, but centrifugal compressors are unsuitable for low molecular weight gases such as hydrogen or helium. The present invention relates, in part, to a hydrogen liquefaction process using neon as a precoolant. For example, neon
It is circulated from a near atmospheric suction pressure of 16 psig to a suitable centrifugal or axial compressor. That pressure is
Although not lower than the 6.27 psia vapor pressure at the neon triple point, it is a higher pressure compatible with good overall thermodynamic efficiency and neon protection. The neon is cooled by expansion through one or more radial-inlet turbo-expanders. Neon is selectively precooled with other cryogens, such as boiling liquid nitrogen, nitrogen carbon dioxide, to increase efficiency. The neon exiting the coldest expander is a cold gas or a two-phase mixture. It also forms a two-phase mixture by expanding across a Juul-Thompson valve with or without resilient heat exchange between the outlet of the coldest turbo-expander and the expansion valve. be able to. It should be noted that the use of reciprocating expanders is not precluded and that capacity, reliability and compactness make turbo-expanders preferred. As for other aspects of the process of the invention, the purified hydrogen is compressed to a pressure above 188 psia critical pressure;
It is pre-cooled mainly by low-pressure circulating neon gas and also by low-pressure circulating hydrogen gas in a multi-pass heat exchanger. Additionally, the hydrogen gas is pre-cooled with liquid hydrogen or other liquefied gases used as precoolants for neon. The means is to change the hydrogen type to 75% ortho and 25% para
The purpose is to catalytically convert the normal composition of the compound into a para-type composition of more than 95% by liquefaction. This conversion from predominantly ortho hydrogen to predominantly para hydrogen requires that the liquefied hydrogen be maintained as a liquid during storage. The final stage of cooling utilizes a dense fluid expander operating at inlet conditions and expansion efficiency to obtain 85-90 mole percent liquid hydrogen product. This two-phase mixture enters a phase separator and the separated liquid fraction is stored while the saturated vapor fraction is recycled to a heat recovery heat exchanger to bring it to ambient temperature for recompression. In addition, the feed is converted to a
Hydrogen concentration increases further. The converted liquid (ortho to para) is then partially cooled to the liquid phase by flashing across a J-T valve and provided as a coolant for the product precooler. As can be seen from the above description, the present invention has two complementary elements: the use of neon as an intercoolant and the use of a dense fluid expander for hydrogen. The use of neon as an intercoolant is practical due to neon's thermodynamic properties. Neon has an atomic weight of 20 and a normal boiling point of -410.4〓 (27.2K, -
248.9°C) and a critical temperature of -379.7〓 (44.1 K, -229°C) at a critical pressure of 395 psia (2723 kPa). Neon is composed of various hydrogen isotopes and oxygen [-
361.8〓(54.0K, -219.1℃)〕, fluorine〓〓〓-363.3〓
(53.2K, −219.9℃)] or CF ₂ [−370〓(49.4K,
-223.7°C)] is the only substance that can exist in a liquid phase between the triple points. For oxygen and fluorine, the triple point vapor pressure of OF ₂ is on the order of 0.01 psia (68.9 Pa), so
They are not considered to represent practical temperature limits. Also, these substances are unfortunately chemically reactive with hydrogen. Neon has a molecular weight of 18
It is practically possible to compress it to an appropriate compression ratio in an appropriate number of stages. Neon is a noble gas and is inert, non-flammable and non-toxic. The dense fluid expander used in the method of the present invention is a machine that discharges the dense fluid contained therein, expands it under reduced pressure, and performs work during this time.
This machine is either a reciprocating piston engine or a turbo expander with a centrifugal rotating wheel; this type of expander is known as an isotropic expander. Valve expansion, on the other hand, is known as Joel-Thomson or isoenthalpic expansion, as no work is done in this type of expansion. The differences between these two expansion means are fully illustrated by the following table.

〔Example〕

In order to illustrate the advantages of the present invention and to contrast it with similar prior art techniques, the following specific examples are provided. Example 1 For the method of the invention as depicted in the only accompanying drawing, 25 mol % of the para-isotope is 75
Gaseous hydrogen, % ortho isotope, was supplied via line 10 and compressed to 650 psia (4480 kPa) in a reciprocating compressor 12. The compressed hydrogen feed stream in tube 14 is mixed with the compressed recycled hydrogen stream in tube 50 to form a mixed hydrogen stream in tube 16 containing 15% by volume of recycled hydrogen. This mixed hydrogen stream in tube 16 is then cooled to −290° C. (−179° C.) in heat exchanger 18, resulting in a cooled mixed hydrogen stream in tube 20, and further in heat exchanger 2.
2, it is cooled to -310〓 (-190°C).
The further cooled mixed hydrogen stream in tube 24 is fed to a first ortho-para catalytic converter 26 which converts a portion of the ortho form of the hydrogen to the para form. Converter 26 also acts as a heat exchanger to further cool the mixed hydrogen stream. The resulting product in tube 28 from the first ortho-para converter is fed to a second ortho-para catalytic converter 30 where it is further converted from ortho to para and further cooled. Ru. Ortho-para converters 26 and 28 collectively convert the mixed nitrogen stream to approximately
From a composition of 64/36 mol%, ortho/para approximately 5/95
Convert to mol% and change the temperature to −404〓(−242℃)
decrease to. The converted hydrogen stream in tube 32 is then expanded into a dense fluid expander, resulting in a two-phase hydrogen stream that is greater than 90% liquid by weight. This two-phase hydrogen stream in tube 36 is fed to separator 38. The liquid is passed through tube 40 as a liquid hydrogen product.
taken from. From dense fluid expander
Pay attention to the leakage of ortho-hydrogen and thermal energy, so that 90 wt% liquid is obtained, but some of the liquid evaporates due to other reasons, and the final liquid yield is about 85 wt%. That is important. The gaseous portion of stream 36 is recycled to converters 30 and 26 via tube 42 to recover any cooling value. The warm circulating flow in the pipe 46 is circulated by a reciprocating compressor 48.
Compressed to 650 psia (4480 kPa) resulting in compressed circulating hydrogen stream 50. Heat exchange for the hydrogen liquefaction cycle is provided by recovering cooling value from the circulating hydrogen stream 42, a neon cooling closed circuit, and warmed liquid nitrogen. The neon refrigeration closed circuit interacts with the hydrogen liquefaction process in heat exchangers 18 and 22 and converters 26 and 30. In the closed circuit, the
The neon stream compressed to a pressure of 150 psia (1034 kPa) is heated to −310〓(−
190℃). This cooled, compressed neon stream in tube 70 is then split into first and second portions. Approximately 58% by volume of the total neon flow in tube 72
In the converter 26, the first portion of is further -
It is cooled to 366.5〓 (-221℃). The cooled first portion in tube 74 is then expanded into turbine 76 to obtain a further cooled first portion in tube 78 at a temperature of -403° (-245 DEG C.). tube 78
This further cooled first portion of the converter 30
at -376.5〓 (-227°C), thereby providing cooling for the process. A second portion of approximately 42% by volume of the total neon flow in tube 82 is expanded into turbine 84 and a cooled second portion at a temperature of -227 DEG C. is obtained in tube 86. tube 8
This cooled second portion in tube 6 and the warm first portion in tube 80 are mixed into the circulating neon stream in tube 88 and at -320° (-196°C) in converter 26.
to provide cooling to the process. In the heat exchanger 18, the circulating neon flow is further increased by 100
(38° C.), the remaining refrigeration value is recovered and fed through tube 92 to compressor 94 of the neon refrigeration circuit. As an additional cooling source, liquid nitrogen and/or cold gaseous nitrogen is heat exchanged in the liquefaction process.
In that implementation, liquid nitrogen in tube 52 is supplied to heat exchanger 22 and warmed, resulting in an at least partially vaporized nitrogen stream in tube 54.
The at least partially vaporized nitrogen stream in tube 54 is mixed with cold saturated nitrogen gas in tube 56 and fed to heat exchanger 18 through tube 58 .
The nitrogen stream in tube 58 is warmed in heat exchanger 18 to recover residual cooling value and then exhausted to the atmosphere via tube 60. The power required to produce 36 tons/day of liquid hydrogen using the method of the invention is 12974 KW, not including the power required to provide liquefied nitrogen and gaseous nitrogen. Table 1 shows the material balance of the process focusing on selected streams.

EXAMPLE 2 In a method as depicted in the only figure of the accompanying drawings, the dense fluid expander was replaced with a Juul-Thompson valve, resulting in the process described in Hosoyama U.S. Pat. No. 4,498,313. I got a result that looks like this. In the method that includes a J-T valve instead of a dense fluid expander, approximately 76
Weight percent liquid production was obtained from the J-T valve.
The energy required to produce 36 tons/day of liquid hydrogen is 14,674KW. Table 2 shows the material balance for Example 2, focusing on the selective flow.

〔Effect of the invention〕

Comparing the results of Example 1 of the present invention and Example 2 of the closest prior art, both methods can produce 36 tons/day of hydrogen, but there is a significant difference in the required power between the two methods. The method of the invention shows approximately 13% energy savings over the method described in Example 2. 2-3 of the power required to liquefy cryogen
% decrease seems to be large. Furthermore, the use of a dense fluid expander in the present invention is demonstrated in Example 2.
A 10.8% reduction in the amount of neon required for the method is obtained. Although the invention has been described in terms of preferred embodiments, the scope of the invention is not limited to these embodiments.

[Brief explanation of the drawing]

The accompanying drawings are schematic diagrams for implementing the method of the invention.

Claims (1)

[Claims] 1. Compressing and cooling a hydrogen stream, catalytically converting predominantly ortho hydrogen to predominantly para hydrogen, the converted, cooled, and compressed hydrogen stream; into an expander, thereby partially condensing the converted hydrogen stream, separating the partially condensed hydrogen stream into liquid and gas phases, and warming the gas phase for cooling recovery and recondensing the converted hydrogen stream. Expanding the converted, cooled, compressed hydrogen stream in a method of liquefying hydrogen by compressing and mixing with the compressed hydrogen stream prior to cooling and removing the liquid phase as a liquid hydrogen product. An improved method as described above, characterized in that it utilizes a dense fluid expander for the process and a closed circuit neon refrigeration cycle to provide at least intermediate cooling to the process. 2. Providing additional cooling for cooling the compressed hydrogen stream or for precooling neon or liquid and cold gaseous nitrogen in a closed circuit neon cooling cycle. the method of. 3 (a) compressing and cooling the gaseous hydrogen feed stream; (b) combining the compressed hydrogen feed stream with the compressed recycled hydrogen stream from step (g) to form a combined hydrogen feed; (c) cooling said combined hydrogen feed stream by heat exchange with a warming circulating hydrogen stream and a closed loop neon cooling cycle; (d) said cooled combined hydrogen feed stream; in two stages of first and second converter/heat exchanger,
converting predominantly ortho hydrogen to predominantly para hydrogen while simultaneously cooling the combined hydrogen feed stream by a closed circuit neon cooling cycle and heat exchange with a warming circulating hydrogen stream; (e) expanding the converted combined hydrogen feed stream into a dense fluid expander, thereby partially condensing the feed stream; (f) converting the partially condensed hydrogen feed stream of step (e) into a gas phase; separating into a liquid phase, using the gas phase to form a circulating hydrogen stream, and further converting the liquid phase to increase the para-hydrogen concentration and removing it as a liquid hydrogen product stream; (g) as described above; warming to recover the cooling of the circulating hydrogen stream and then compressing said circulating hydrogen stream before combining said compressed hydrogen feed stream of step (b); (h) compressing a closed circuit neon cooling stream and preparing a reserve; (i) splitting said closed circuit neon cooling stream into a first portion and a second portion; (j) further cooling said first portion and then said cooled first portion; (k) warming said first part from step (j) in said second converter/heat exchanger, thereby providing cooling; (l) said second part from step (j); expanding the portion into an expander and combining the expanded second portion with the warm first portion from step (k) to form a recombined closed circuit neon cooling stream; (m) warming said recombined closed circuit neon cooling stream in said first converter/heat exchanger thereby providing cooling; (n) further heating said recombined closed circuit neon cooling stream; and (o) recycling said recombined closed circuit neon cooling stream to step (h) as said closed circuit neon cooling stream. 4. The method of claim 3, further comprising providing cooling for said cooling in step (c) and for precooling in step (h) with liquid nitrogen and cold gaseous nitrogen.